This function takes an n-dimensional input array of the form
[max_sequence_length, batch_size, other_feature_dims] and returns an array of the same shape.

Parameter sequence_length is used to handle variable-length sequences. sequence_length
should be an input array of positive ints of dimension [batch_size].
To use this parameter, set use_sequence_length to True,
otherwise each example in the batch is assumed to have the max sequence length and
this operator works as the identity operator.